Rotor for electric motors



E. Gv. FAHLMAN ROTOR FOR ELECTRIC MOTQRS Filed July 7, 1932 INVENTOR Everett BY E X/lc ATTORNEYS C53/ A Patented .im 4, 193s j UNITED sTATEs PATENT OFFICE i Thelermold porationolohio Ohio, a oor- ADMII Jill! 7 1.32, N0. 21,183

, I. v 1 claim.A (ci. 17a-1z0) My invention relates to rotors for electric motors, andmoreparticularlytorotorshavingcastconductor bars or end rings formed of a conductive metal or alloy. 'Thisapplicationisacontinuationinpartof my upplicaidon Serial No. 558,056, iiled on August 19, 1931.

An object of my invention is to provide an integral cast rotor structure having improved electrical characteristics.

Another object of my invention is to provide a rotor having a thin layer of heat and electrical insulating material interposed between the core of the rotor and the conductor bars.

A further object of my invention is to provide a rotor in which the conductor hars are formed of commercially pure, electrolytically refined alu- A still further object of my invention is to provide a rotor having a core with longitudinal pas' sages coated with a layer of electrical and heat insulating material so that when a conductive metal, such as aluminum or aluminum alloys, is cast in the passages to form conductor bars, the insulating material will serve as a heat insulating material during the casting operation and act as an electrical insulator between the conductor bars and the core in the finished rotor.

Another object of my invention is to provide an improved rotor structure having conductor bars and end rings formed of a conductive metal, such as aluminum or aluminum alloys, the conductor bars being insulated from the Ycore of the rotor in such a manner that the rotor will have improved electrical characteristics.

A still further object of my invention is to provide an improved rotor having a laminated core formed of ferrous material and conductor bars or end rings formed of a conductive metal, such as aluminum or an aluminum alloy, the conductor bars being insulated from the laminated material in-such a manner that the rotor shall have improved electrical characteristics. v

In forming rotors for electrical motors having a core formed of ferrous material, such as iron or a ferrous alloy, and conductor bars and end rings formed of aluminum or an aluminum alloy, it has been the practice to cast conductor bars in es or slots formed in the laminations andtocast endrings adjacentto the outer marginoftheendlaminationstoformanintegral structure. In order, however, to produce castings having lmiform electrical and physical propertles, it is highly desirable to introduce the metal lmiformly at substantially the same temperature throughout the casting cavity and to regulate the, cooling so that the conductor bars shall have uniform electrical and physical properties. When I aluminum or aluminum alloys are cast in the con- 'ductor bar cavities formed in iron or ferrous alloys, the high heat conductivity of the adjacent ferrous metal has the tendency to cool the molten casting metal very rapidly and castings are produced having voids, cold shuts and other imperfections. It is, of course. desirable that the metal should cool fairly rapidly in order that the castings shall have a iine grain structure, but if the cooling is too rapid, satisfactory castings will not be produced.

Ihavemadethediscoverythatifthelamina- 1B tions of the rotor are assembled in aligned relationship, the assembly heated to a comparatively high temperature. and a thin coating of a heat and electrical insulating material is sprayed or otherwise applied to the ferrous metal surrounding the longitudinal passages before the casting operation is performed, the insulating material will prevent too rapid cooling of the casting metal and conductor bar castings may be produced which are free from voids, cold shuts and other imperfections. The electrical insulating property of the material is also instrumental in providing a rotor having improved electrical characteristics.

This feature not only enables the use of aluminum or aluminum alloys but renders it possible to employ other metals having a comparatively high conductivity. such as copper, magnesium or certain of their alloys. I prefer, however, to utilize aluminum or aluminum alloys, because they may be cast at a comparatively low temperature and have a comparatively high conductivity. In view of its' high conductivity, electrolytically reilned aluminum is highly desirable.

My invention will be better understood by reference to the ying drawing, in which: 40

Figure 1 is a perspective view of a rotor core showing the laminations disposed in aligned relationship, and means for providing an insulating coating in the conductor passages;

Pig. 2 is an elevational view, partly in cross sec- 45 tion. oi' my improved rotor showing the end rings and conductor bars;

Flg.3isanendviewoftherotorshowninl*ig. 2; and

Fig.4isanenlargedplanviewofalaminae5 am Yz in which conmutar bm a formed of 5 aluminum or aluminum alloys are cast. End rings 4 formed of aluminum or aluminum alloy are also cast around the peripheral margin of the end laminations, and the conductor bars and end rings serve to hold the laminations in place. 'Ihe rotor is also provided with a central shaftreceiving aperture 5, slotted apertures 6 arid an aperture 1. l

In manufacturing my improved rotor, the laminations are placed upon a mandrel 9 so that the slots may be in aligned relationship. The laminations are then heated to a temperature of approximately 250 to 300 F., and a solution of a heat and electrical insulating material is sprayed downwardly through the passages and around the peripheries of the rotor, as illustrated in Fig. 1 of the drawing, by means of a suitable spray 8. Instead of spraying the material in the passages, however, the assembled laminations and mandrel may be dipped in an aqueous suspension of the electrical and heat insulating material. If the slots or passages are spaced from 'the periphery, it will of course be understood that the insulating material will be sprayed directly through the slots or passages in which case it will not be necessary to spray the outer pe-v ripheral surface of the rotor with insulating material. The heated laminations cause the coating to dry quickly, and a thin smooth lining of -the heat and electrical insulating material I is formed on, and closely adheres to, the surface of the metal surrounding the slots and the outer periphery of the laminations.

While I do not desire to be limited to any particular heat and electrical insulating material, I have found that a suspension of aluminum oxide, or a suspension of china clay, in an aqueous solution of sodium silicate, are suitable. A suspension of china clay in an aqueous solution of sodium silicate not only acts as a good heat insulating medium during the casting operation, but serves as an excellent insulator in the finished rotor. I have found that if the assembled laminations are rst heated to the temperature' specified and the walls of the passages are sprayed with such a suspension, the coating will dry rapidly and a thin uniform layer of a heat and electrical insulating material will be provided which closely adheres to the walls of the conductor bar passages.

After the heat insulating layer has been applied, the laminations are heated to a temperature of approximately 600 to 1000 F., placed in a mold, and molten aluminum or aluminum alloy is poured into or caused to flow upwardly through the conductor bar passages, and into the mold cavities, to form the conductor bars and end rings. The particular temperature to which .the laminations are heated will depend upon the volume of the laminations, the volume and surface area of the conductor bars to be cast, and the surface area of the mold. Before the laminations are placed in the mold, the mold is also heated to a. temperature of approximately 600 to 1000 F., depending upon the temperature to which the laminations are heated, in order that the chilling effect of the mold will not tend to cause cold shuts and the like b'ut yet may be suilicient to cause the metal to solidify under advantageous permanent mold conditions. The mold is generally heated to a temperature approximating but usually exceeding the temperature of the laminations. After the mold has been heated for the rst casting in a run, the heat imparted to the mold from the poured casting metal and the heated laminations is ordinarily sufiicient to maintain the mold at the proper molding temperature. As a rule, the temperature of the mold will be considerably less than the temperature of the laminations and will vary through a temperature cycle during the casting operation of some magnitude. While the optimum temperature towhich the laminations of rotors o f different construction should be heated varies over a considerable temperature range in accordance with the factors specified, the temperature to which the laminations of a rotor of specified construction or a series of rotors of approximately the same construction shouldbe heated before the castingoperation, is held within a comparatively narrow range. For example, after the optimum temperature to which the laminations should be heated has been ascertained, the heating temperature to which the laminations of the rotor, orv other rotors of a similar construction are heated before the casting operation, is not permitted to vary more than approximately 50 F. from that temperature.

In view of the heat insulating properties of the lining and because the laminations are heated to a comparatively high temperature,.the cooling of,l the metal in the conductor bar passages is retarded and castings free from voids, cold shuts and other imperfections will be produced.

By the use of a heat insulation and by separately heating the assembled laminations of the rotor to a temperature which is usually higher than the mold before placing the assembly therein, it is possible to form rotors with a cast conductor system of commercially pure aluminum containing less than 1% total impurities or even electroyltic aluminum in which the impurities are less than .25%. In previous practice, it has heretofore not been possible to utilize commercially pure aluminum of such a grade of purity or electrolytic'relined aluminum because of the diiilculty of casting the metal. It is preferred, however, in the manufacture of rotors to utilize commercially pure aluminum because substantially pure aluminum has a greater electrical conductivity than aluminum alloys or aluminum containing larger amounts of impurities. Furthermore, when metal of greater conductivity is employed, the cross sectional area ofthe conductor bars may be reduced, which permits the use of a greater amount of magnetic material in the rotor.

It is well known, however, that pure aluminum is more difcult to cast than aluminum alloys or aluminum containing a larger amount of impurities because of its higher crystallization shrinkage. The heating of the laminationslbefore being placed in the mold and the use of the insulations renders the formation of rotors having conductor bars formed of commercially pure or electrolytically refined aluminum not only possible but commercially practicable.

In forming the castings, I' prefer to cause the molten metal to flow into the lower end ring cavityto form the end ring l, and upwardly through the conductor bar passages to form the conductor bars, and into an upper end ring cavity to form the end ring E' as disclosed in my application Serial No. 558,056 filed on August 19, 1931, of which this application is a continuation in part.

From the foregoing specification, it will be apparent that the insulating material in the conductor bar passages performs a dual function; that is, provides a heat insulating coating during the casting operation to prevent too rapid cooling of the metal, and serves as an electrical insulation in the finished rotor. A rotor having improved phil and electrical properties is therefore provided.

`It will also be seen that my invention provides Aa unique'manner for controlling casting conditions, whereby castings heretofore tormed with dimoulty may be produced commercially.

Furthermore, it will be noted that the casting metal in the slots and end rings also serves to hold the laminations in position, thus providing a substantially integral structure.

It will further be noted that by my invention I have provided an integral cast rotor for induction motors involving new and improved electrical characteristics, whereby an electric circuit of uniform conductivity and hence uniform torque may be obtained.

Furthermore; it is to be understood that the particular form of apparatus shown and described is presented for purposes of explanation and illustration, and that various modifications can be made without departing from my invention as defined in the appended claim.

What I claim is:

A rotor comprising a laminated core formed of ferrous material having a plurality of circumferentially arranged conductor bar passages extending through said laminations, an integral casting selected from a group comprising cast aluminum and a cast aluminum alloy disposed in and substantially iilling said passages and a re1- atively thin coating of chain clay adherently secured to the walls of said passages with silicate o! soda. i

EVERET'I G. FAHLMAN.

CERTIFICATE or coRREcTiou; Paten: No. 2,003,587. 'June-4. 193s.

l EVERETT G. FAHLMAN.

It Vis hereby certified that error appears in the printed specification of the above numbered batentrequiring correction as follows: Page 3, -second column, line 14, vthe claim, for "chain" read China; and that the said Letlters Patent should be read with this correction therein that the same may conformito the record of the case in the Patent Office.

Signed and sealed this 9th day of July, A. D. 1935.

Bryan M. Battey (Sell) Actingommissioner of Patents,

CERTIFICATE oF coluuccrionr.v Patent No. 2, 003, 587. Janes, 193:5.

' EVERETT c.A FAIHMAN.

It `is herebu certified that error appears in the printed specification of the A above numbered patentrequiring correction as follows: Page 3, -second column,

line 14, the claim, for "chain" .read China; and that the said Letters Patent should be read with this correction therein that the same may conform'to the record of the case in the Patent Office.

Signed and sealed this 9th davy of July, A. D. 1935.

. c Bryan M. Battey (Seal) Acting'(Iommissioner of Patents, 

